Dynamic correlation effects on drag resistivity of a symmetric electron–electron bilayer

We have studied the effect of dynamic electron correlations on Coulomb drag in a low density symmetric electron–electron bilayer. The drag resistivity is calculated considering the contribution from direct e–e scattering processes using the semi-classical Boltzmann approach, with the effective inter-layer interaction W₁₂(q, ω; T) determined within the ?wierkowski, Szyman?ki, and Gortel model, generalized to include the dynamics of electron correlations through the frequency-dependent intra- and inter-layer local-field correction (LFC) factors. In turn, the LFCs are obtained by extending the quantum Singwi, Tosi, Land, and Sjölander (qSTLS) approach to finite temperatures. At low temperatures (T ? 2 K), the calculated drag resistivity is found to agree nicely with the measurements by Kellogg et al., while it is somewhat overestimated at higher temperatures. The overestimation is seen to increase with decreasing density of electrons. However, there is found to be a marked improvement over the predictions of the conventional (i.e., static) STLS and random-phase approximation (RPA). It turns out that the inclusion of exchange-correlations in the RPA causes a red-shift in the bilayer plasmons which leads to an enhancement of drag resistivity. Our study demonstrates clearly the importance of including the dynamical nature of correlations to have a reasonable account of measured drag resistivity.     

Detection-theoretic analysis of the observer-based psychophysical procedure

The observer-based procedure, used in research applications to measure the hearing sensitivity of young infants, is analyzed within the framework of a two-stage (infant-judge) detection model involving a minimum number of assumptions. The model is taken to develop convergence theorems useful for estimating the number of judges and/or trials required to achieve a desired level of accuracy using the procedure. The model is also used to consider ways in which bias in estimates, known to be associated with the procedure, might be evaluated and reduced. Finally, a method is proposed by which the results of the analysis and different procedural variations designed to improve estimates can be evaluated empirically.     

Comparative analysis of continuous cooling transformation behaviour in CGHAZ of API X-80 and X-65 line pipe steels

Journal of Thermal Analysis and Calorimetry - Continuous cooling transformation diagrams were obtained for a simulated coarse-grain heat-affected zone of API X-80 and X-65 steels using Gleeble-3800...     

Crystallization and optical properties of CaWO4 and SrWO4

Single crystals of calcium tungstate and strontium tungstate have been grown by double decomposition flux reaction technique using lithium chloride as flux. Growth conditions are optimized to synthesize well faceted crystals. Effect of primary and secondary flux density in the growth charge has been studied. Thermogravimetric study reveals that the grown crystals are highly stable in the temperature range 25 – 1000°C. Analysis of optical absorption normal to the ab‐plane in the spectral range of 200 – 800 nm reveals the true absorption edge, the nature of transition being the allowed indirect one at 4.60 eV and 4.56 eV respectively for CaWO₄ and SrWO₄. The crystals have been characterized by determining useful pertinent optical and dielectric parameters. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Application of orthogonal collocation on finite elements for solving non-linear boundary value problems

A simple, convenient and easy approach to solve non-linear boundary value problems (BVP) using orthogonal collocation on finite elements (OCFE) is presented. The algorithm is the conjunction of finite element method (FEM) and orthogonal collocation method (OCM). The stability of the numerical results is checked by a novel algorithm which not only justifies the stability of the results but also checks the convergence of the method. The method is applied to the non-symmetric boundary value problems having Dirichlet’s and mixed Robbin’s boundary conditions.     

A TAGE iterative method for the solution of non-linear singular two point boundary value problems using a sixth order discretization

We report two parameter alternating group explicit (TAGE) iteration method to solve the tri-diagonal linear system derived from a new finite difference discretization of sixth order accuracy of the two point singular boundary value problem , 0 < r < 1,  = 1 and 2 subject to boundary conditions u(0) = A, u(1) = B, where A and B are finite constants. We also discuss Newton-TAGE iteration method for the sixth order numerical solution of two point non-linear boundary value problem. The proof for the convergence of the TAGE iteration method when the coefficient matrix is real and unsymmetric is discussed. Numerical results are presented to illustrate the proposed iterative methods.     

Thermochemical studies on the formation and constitution of the zinc oxide—aluminium oxide system

This study is based on thermogravimetric (TG), differential thermal analysis (DTA) and chemical analysis of the ZnOAl₂O₃ system. The coprecipitation from mixed nitrate salt solutions of zinc and aluminium results in the formation of zinc basic carbonate and aluminium hydroxide, and is also a precursor to aluminate spinel (2ZnO·3Al₂O₃) only in the samples in which aluminium is present in near or above stoichiometric quantities. Grinding of the mixtures of individual precipitates maintains the similarity with coprecipitates in forming a “precursor”, but to a lesser extent. The endothermic peak in DTA at 275°C in some coprecipitated and mixed samples hints at the formation of a precursor since the individual precipitate does not have a peak at this temperature. The “precursor” to spinel obtained in the precipitation stage in some coprecipitated samples is freely soluble in 1 M HCl, and that obtained at 450°C is partially soluble which cannot be detected by the usual X-ray technique due to its highly disordered structure in amorphous state. The “precursor” is converted around 800°C to an actual spinel structure, which is almost insoluble in M HCl and is detectable by X-rays.     

Photophysical investigations of interpolymer interactions in solutions of a pyrene substituted poly(acrylic acid), poly(vinyl amine), poly(1-aminoacrylic acid), and poly(1-acetylaminoacrylic acid)

Photophysical properties of the pyrene chromophore covalently bound to poly(acrylic acid) were used to investigate the interactions of a pyrene substituted poly(acrylic acid) (1) with poly(vinyl amine hydrochloride) (PVAm), poly(1-aminoacrylic acid) (PDA), and poly(1-acetylaminoacrylic acid) (PADA) in aqueous solutions. A number of photophysical parameters were obtained from fluorescence emission and excitation spectra, the deconvolution of decay curves for pyrene monomer, and excited state complex fluorescence and the quenching of pyrene monomer fluorescence by nitromethane in polymer solutions. These photophysical parameters were considered to reflect the inter- and intrapolymer interactions in solutions of 1 , PVAm, PDA, and PADA. The formation of interpolymer complexes between 1 and PVAm was noticed at low (< 4) as well as high (> 8) values, whereas PDA and 1 formed interpolymer complexes at low pH only. No interpolymer complex formation was detected in solutions of 1 and PADA under low or high pH conditions. The structures of interpolymer complexes formed between 1 and PVAm under low and high pH conditions were found to be determined by the conformation of 1 . There were significant differences in the interpolymer interactions of 1 and PDA in comparison to those of 1 and PVAm; in particular, the fluorescence from the excited state complex was enhanced in solutions of 1 and PVAm but quenched in solutions of 1 and PDA. The investigations of terpolymer solutions of 1 , PVAm, and PADA indicated that the nature of interpolymer complexes formed in terpolymer solutions was determined by Coulombic interactions of the amino and carboxylic group containing polymers.